1. Field of the Invention
The present invention relates generally to semiconductor wafer processing apparatus, and in particular, to an improved physical vapor deposition chamber that reduces the amount of unwanted or undesirable metal particles that may be introduced into the chamber during processing of the wafer.
2. Background Art
Semiconductor wafer processing is a complex procedure performed by semiconductor wafer processing systems that can include many chambers where the semiconductor wafers are processed. An example of an available semiconductor wafer processing system is the Endura 5500 that is currently made by Applied Materials, Inc. which is located at 3050 Bowers Avenue in Santa Clara, Calif. Although there are other currently-available semiconductor wafer processing systems, all of these systems include similar chambers and process the wafers in similar manners.
FIG. 1 is a top view of the Endura 5500 system 10. Referring to FIG. 1, the system 10 includes a plurality of chambers, described in detail below, and two robot devices that move the wafers from one chamber to another. The system 10 has two wafer load locks 12, 14 into which wafers are loaded at the beginning of, and at the end of, the processing inside system 10. In particular, plastic cassettes can be placed into these locks 12, 14, with the plastic cassettes adapted to hold the wafers. In operation, a cassette holding a number of wafers is first placed into the first load lock 12 by an operator. A first robot device 16 then removes the wafers from the first load lock 12 and places the wafers into an "orient and de-gas" chamber 18. The "orient and de-gas" chamber 18 orients the notch on the wafers and desorbs gas from the wafers while also slightly pre-heating the wafers. Thereafter, the first robot device 16 removes the wafers from the "orient and de-gas" chamber 18 and places the wafers into one of three etch chambers 20a, 20b or 20c, where an etch can be applied (if necessary) to the wafers, such as through the use of RF plasma.
After etching, a second robot device (not shown) located under top cover 22 removes the wafers from the etch chamber 20c and places the wafers into one or more selected physical vapor deposition (PVD) chambers 24a, 24b, 24c, 24d. Each PVD chamber 24 applies a different type of metal (e.g., titanium, titanium nitride 101, aluminum, titanium nitride clamped, among others) to the wafers to form the interconnect metal lines. The application of metal is done at high temperatures, such as from 200 to 300 degrees Celsius in the Endura 5500 system. If it is desired to apply only one type of metal to the wafers, then the wafers are only placed in the one chamber 24a, 24b, 24c or 24d containing that type of metal. Similarly, if it is desired to apply three types of metal to the wafers, then the wafers are only placed in the selected chambers 24a, 24b, 24c or 24d containing the three specific types of metal. Likewise, if it is desired to apply four types of metal to the wafers, then the wafers are sequentially placed in all the chambers 24a, 24b, 24c and 24d. The second robot device simply removes the wafers from one chamber 24 and places the wafers into the next desired chamber 24, and repeats this operation until the wafers have been processed in all the desired PVD chambers 24. In other semiconductor wafer processing systems, it is possible to provide any number of these PVD chambers, with such number typically ranging from one to six.
When all the desired metal types have been applied to the wafers, the second robot device will remove the wafers from the last PVD chamber 24 where metal was applied, and places the wafers into a cool chamber 26, where the wafers are cooled. A gas, such as Argon, is introduced into the cool chamber 26 to produce a conduction medium to pull heat away from the wafers. The wafers must be cooled after processing, otherwise the high temperature of these wafers will melt the plastic cassettes that are located in the second wafer load lock 14. After cooling, the first robot device 16 picks up the wafers, removes them from the cool chamber 26, and places the wafers into cassettes in the second wafer load lock 14, where the wafers are stored until removed by the operator of the system 10.
The PVD chambers 24 have a generally square configuration (with rounded comers) with a generally oblong opening or mouth. Referring to FIG. 2, the mouth or opening of the PVD chamber 24 is defined by a spacer 30, which is typically bolted or otherwise attached to the wall of the chamber 24. The spacer 30 is generally made of a metal, such as aluminum or stainless steel. The spacer 30 is used to receive an insulator 44 (described below) and to adjust the heater of the system 10 to target spacing distance. A target 32 is placed over the insulator 44 which is in turn placed within a groove 52 of the spacer 30. The target 32 is the metal that is to be sputtered for deposition onto the wafers, and examples of such metals can include titanium, titanium nitride 101, aluminum, and titanium nitride clamped, among others. The target 32 is typically provided in a circular shape having a trapezoidal central portion 34 and an annular flange 36. In one example, the central portion 34 has two inclined or angled walls 38, 40. The flange 36 is provided as an overhang to fit over the spacer 30, so that the central portion 34 can extend through the opening of the chamber 24 defined by the spacer 30. The target 32 can be provided either in the form of one piece of the desired metal, or in a "diffusion bonded" manner, where the desired metal shaped as the central portion 34 is attached to a backing (made of aluminum or other materials) that extends throughout the top 42 of the target 32 and includes the flange 36. A "diffusion bonded" target 32 is lower in cost since the entire piece of the target 32 does not need to be made of the desired metal, which can be more expensive than aluminum or the selected material. A fiberglass composite top is then provided over and bolted to the backing (i.e., the top 42) of the target 32. When the PVD chamber 24 is in use, water is typically used to cool the back side (i.e., the top 42) of the target 32 to minimize warping of the target 32, and to prevent the target 32 from melting.
An insulator 44 is provided between the target 32 and the spacer 30 to isolate the "cathode" (i.e., the target 32) from the "anode" (i.e., the spacer 30). In particular, the insulator 44 partially sits in a groove 52 provided in the spacer 30. This isolation is required to provide a voltage potential between the anode and the cathode. This insulator 44 can be a ceramic material, such as alumina. The insulator 44 also operates as a vacuum sealing surface. In addition, a first O-ring 46 is provided to separate the insulator 44 and the spacer 30, and a second O-ring 48 is provided to separate the insulator 44 and the flange 36 of the target 32. The O-rings 46, 48 are provided as a seal to prevent leaks.
The structure of the PVD chamber 24 shown and described in FIG. 2 suffers from the drawback that undesirable metal particles from the target 32 may be discharged into the interior of the PVD chamber 24. Since a vacuum is pulled towards the inside of the PVD chamber 24 in the direction of arrow 50 when the PVD chamber 24 is in use (the vacuum is pulled to reduce impurities), the O-rings 46, 48 tend to be compressed and typically will collapse to a point where the opposite sides of the insulator 44 contact the target 32 (at the flange 36) and the spacer 30. The contacting surfaces undergo slight side-to-side movement caused by chamber vibration, pumping and venting of the PVD chamber 24, and deformation changes in the O-rings 46, 48 when the chamber is periodically opened for preventative maintenance (also known as the initial pump-down sequence). In addition, since the materials used for the target 32 (e.g., a metal), the insulator 44 (e.g., ceramic) and the spacer 30 (e.g., aluminum) have different thermal expansion rates, the linear compression created by reducing the chamber pressure and the side-to-side movement causes particles from the target 32 to be imbedded into the material of the insulator 44. As a result, when the entire assembly illustrated in FIG. 2 (including the insulator 44 material) is re-heated during the processing of the next batch of wafers, further abrasive activity resulting from the side-to-side movement of contacting surfaces may cause the previously imbedded particles to fall off from the insulator 44 and to be deposited into the PVD chamber 24. It is also believed that the embedded metal particles may cause the material of the insulator 44 to become semi-conductive, thereby creating a "micro-arc" (i.e., a small isolated discharge) which might result in the further discharge of undesirable particles into the PVD chamber 24.
The discharge of unwanted metal particles into the PVD chamber 24 results in reduced product yield because such discharge will increase the deposit of non-homogeneous metal onto the wafers, thereby producing defective or otherwise unusable dies on a chip produced from the wafer. These undesirable particles can further reduce or break predetermined conductive paths.
Thus, there still remains a need for an improved PVD chamber that reduces the amount of unwanted or undesirable metal particles that may be introduced into the chamber during processing of the wafers.